Question

Which one of the following is an example of heterocyclic aromatic compound?

• A. Phenol
• B. Aniline
• C. Toluene
• D. Naphthalene
• E. Pyridine

Hint:

Heterocyclic aromatics: Pyridine (N), Pyrrole (N), Furan (O), Thiophene (S).

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
The question asks to identify a heterocyclic aromatic compound. This requires understanding two terms:
- Heterocyclic: A cyclic compound where at least one atom in the ring structure is an element other than carbon. This other atom is called a heteroatom (e.g., oxygen, nitrogen, sulfur).
- Aromatic: A cyclic, planar compound with a continuous ring of p-orbitals that follows Hückel's rule, having (4n+2) \(\pi\) electrons, where n is a non-negative integer.
Step 2: Analysis of Options:
Let's analyze each option:
(A) Phenol, (B) Aniline, and (C) Toluene are all derivatives of benzene. Benzene is a carbocyclic (or homocyclic) compound, meaning its ring is made up entirely of carbon atoms. Thus, these are not heterocyclic.
(D) Naphthalene consists of two fused benzene rings. It is aromatic but also carbocyclic/homocyclic.
(E) Furan has a five-membered ring structure containing four carbon atoms and one oxygen atom. Since the ring contains a heteroatom (oxygen), it is a heterocyclic compound. Furan is also planar, cyclic, has a conjugated system, and possesses 6 \(\pi\) electrons (4 from the two double bonds and 2 from one of the lone pairs on the oxygen atom), which satisfies Hückel's rule for n=1. Therefore, furan is a heterocyclic aromatic compound.
Step 3: Final Answer:
Furan is the only compound in the list that is both heterocyclic (contains oxygen in the ring) and aromatic. This corresponds to option (E).